1. Field of Invention
The present invention relates to a power transmission mechanism, and more particularly to a power transmission mechanism applied in a multi joint robot arm.
2. Related Art
The robot or robot arm has been widely applied in various different fields such as production and manufacturing, warehouse management, and intelligent nursing. The robot or robot arm is usually formed by a structure with a plurality of support arms connected together. The pivoting motion of each support arm is controlled by driving joints connecting the support arms.
During motions of a robot arm, a joint is rotated by using a rotating power provided by a motor. The power of the motor is output via a speed reducer to realize a relatively large torque. In a conventional robot arm, each motor is directly mounted on each joint. However, if each motor is directly mounted on each joint, each joint has a more complicated structure and bears an increased load, and as a result, the robot arm rotates under a large inertia. Furthermore, it is also quite difficult to configure lines of the motors, in order to prevent the lines of the motors from being wound together.
In order to solve the aforementioned problems, for example, U.S. Pat. No. 5,207,114 has disclosed “COMPACT CABLE TRANSMISSION WITH CABLE DIFFERENTIAL”, in which a four-axially-driven robot arm is provided, and mainly uses steel ropes as a power transmission medium. In U.S. Pat. No. 5,207,114, the motor is disposed on the lower layer of the robot arm, and transmits power through the steel ropes, so as to solve the problems caused when the motor is directly mounted on each joint. However, in order to prevent too many steel ropes from winding together during power transmission, as disclosed in U.S. Pat. No. 5,207,114, the motor transmits power to a coupling member (marked as 24 in FIG. 8) via two steel ropes (marked as 19ra and 19rb in FIG. 8), such that the link arm (marked as 18 in FIG. 8) only has one degree-of-freedom, thereby motions of the robot arm are restricted.
Furthermore, the length of the support arm of the robot arm is just the working range of the robot arm, and the longer the support arm is, the wider the working range will be. However, if the support arm becomes longer, the steel ropes also become longer, i.e., the load of the steel ropes becomes heavier. Thus, it is necessary to adjust the tension of the steel ropes frequently, so as to reduce power transmission loss. Unfortunately, the service life of the steel ropes is shortened accordingly.